Medical Parasitology — Notes OmpathStudy

MEDICAL ENTOMOLOGY Vector Control Methods 1. Physical/Mechanical Control Screened windows and doors Mosquito nets on walls Draining pools of water Removing long grass Emptying containers 2. Biological Control Using living organisms to control vectors Toxorhynchites mosquito species - larvae feed on larvae of Anopheles, Culex, and Aedes Gambusia affinis (fish) - feeds on mosquito larvae Bacillus thuringiensis (Bt bacteria) - bacterial form Bacillus sphaericus Other predators 3. Genetic Engineering Sterile male technique Refractory vectors - modifying genes of vectors so that pathogens cannot develop Result: change in target site 4. Chemical Control - Insecticides Classification Based on Toxicity (LD50): LD50 1-50 : Extremely toxic/dangerous LD50 50-500 : Moderately toxic LD50 5000 : Safe Types of Insecticides: A) Chlorinated Hydrocarbons Relatively stable Act as nerve poisons Lipid/fat soluble Disrupt Na+ channels Most are banned (e.g., DDT) due to long persistence and bioaccumulation in fatty tissues Examples: DDT, Dieldrin, Endrin B) Organophosphates (OP) Less persistent, don't accumulate in fatty tissues Block cholinesterase (acetylcholine won't be broken down) Examples: Malathion, Chlorpyrifos, Parathion, Diazinon, Dimethoate C) Carbamates MOA similar to organophosphates Bind to acetylcholinesterase Better biodegradability, availability, and solubility Examples: Carbaryl, Propoxur, Bendiocarb Lower mammalian/human toxicity Advantage over OP : Chronic exposure to carbamates is less likely to cause illness than organophosphates; inhibiting action is reversible D) Pyrethroids Synthetic/semi-natural compounds Examples: Permethrin (used in ITNs, LLINs), Deltamethrin They bind to voltage gated sodium channels and delay their inactivation. increasing permeability Results in excitation, lack of coordination, and paralysis Relatively safe for outdoor use Effect is rapid (knockdown effect) E) Insect Growth Regulators (IGRs) Block insect sugar/chitin biosynthesis pathway Example: Pyriproxyfen, Diflubenzuron F) Formamidines Mimic activity of octopamine (neurotransmitter/neurohormone/neuromodulator) They bind to octopamine receptors in insects, leading to disordered neuronal excitation and death MOA is different, useful in resistant insects Example: Amitraz Effective against mites and ticks Examples: Chlordimeform, Amitraz G) Avermectins Cause paralysis and death by inhibiting transmission of nerve impulses Narrow spectrum, active only against specific invertebrates Can also be used against parasitic nematodes Example: Abamectin H) Neonicotinoids Both systemic and contact activity against sucking insects Mimic nicotine Example: Imidacloprid I) Miticides Effective against mites Examples: Bromopropylate, Cyhexatin, Tetradifon Types of Insecticides by Application: Contact poison Fumigant Systemic Stomach poison Respiratory poison --- MOSQUITO-BORNE DISEASES Family: CULICIDAE Genus: ANOPHELES Key Species: Anopheles gambiae complex (supervector) An. funestus An. arabiensis - zoophilic An. melas An. stephensi - supervector, transmits malaria mostly in Asia; recently reported in Africa (unlike other African species, can withstand high temperatures and arid conditions) Behavior: Anthropophilic Endophagic (feeds indoors) Endophilic (rests indoors) Life Cycle: Complete metamorphosis (holometabolous) Duration depends on temperature (optimal 25°C) and humidity (78%) Breeding: Stagnant water with vegetation and algae Eggs laid singly and laid one at a time Float on water surface Larval Stage: 4 instars (L1-L4) Larva lies parallel to water surface (breathes through spiracles on body side) Feeding stage Pupal Stage: Resting stage Comma-shaped Emerges after 2-3 days Adult Stage: Emerges and mates post-emergence Females : Feed on sugar solutions AND blood (require blood meal for egg development - anautogenous) Males : Only feed on sugar solutions Parthenogenesis possible (egg development without fertilization) Identification: Resting position : 45° angle to surface Antennae : Males - bushy/plumose; Females - smooth/pilose Feeding : Only females take blood meals Both sexes feed on sugar solutions Geographic Distribution: Determined by location of parasite Medical Importance: Primary : Transmission of malaria (genus Plasmodium ) Control Measures: Chemical : Larvicides, breeding site treatment Biological : Toxorhynchites species (T. rutilus) prey on mosquito larvae Genetic : Refractory index - use of endosymbionts/bacteria that kill mosquito, preventing Plasmodium survival Physical/Mechanical :Draining/removal of containers Mosquito nets IRS (Indoor Residual Spraying) Trans-ovarian light traps Screening windows Cutting tall grass/weeds Mesh on walls --- Genus: CULEX Key Species: Culex quinquefasciatus Behavior: Exophagic (feeds outdoors) Exophilic (rests outdoors) Feeding time: 3pm-6pm, nocturnal Diurnal feeding: 10am Breeding: Contaminated water (sewage, drains) Life Cycle: Complete metamorphosis Eggs, larvae, pupae, adult stages Eggs